Wherever high energy radiation is used, for radiotherapy, industrial applications, materials testing, and high energy physics, the amount of energy deposited in matter (dose) needs to be quantified. Traditionally, dosimetry measurements of high accuracy involve off-line instrumentation evaluating the effects of radiation on films (radiographic or radiochromic), thermo-luminescent (TL) or semiconductor devices. Ionization chambers, optical devices and semiconductor devices also allow on-line, real-time dose measurement.
Examples of well known prior art relating to this invention include thermo-luminescent dosimetry (TLD) based on a TL material whereby high energy radiation deposits an electrical charge into energy levels within the bandgap of the host wide-bandgap TL semiconductor doped with an appropriate “color center” impurity element. An example of a thermo-luminescent (TL) material is calcium fluoride doped with Mg, Cu and P. A TL dosimeter material is generally sensitive to exposed energy over a range from 100 kev upward into Gev levels and with exposure to dose levels in hundreds of Gray. When stored at ordinary temperatures, the trapped charge stored within the TL sensor as a result of irradiation is semi-permanent. When a TL semiconductor is heated to temperatures in the range 150 to 600 degrees Centigrade the internal stored charge is dissipated through radiative recombination processes light is emitted. This light is usually in the ultraviolet or deep blue wavelength range. The light so emitted is detected generally with a photomultiplier tube and the resulting response signal is correlated against calibration data to specify the radiation dose.
Another example of prior art dosimetry is based on a sensing of high energy depositions directly within a semiconductor device of material typically of silicon. In the case of an MOS transistor (MOST) as the sensing element in a dosimeter, deposited charge creates and fills energy levels within the amorphous gate dielectric such as silicon dioxide. The sensitivity of gate oxide to radiation increases as the area and volume of the gate dielectric increases. The charge deposited by radiation changes the gate voltage threshold in the MOST. This change of threshold is semi-permanent at room temperature. The change of threshold voltage is determined by monitoring the current-voltage (IV) characteristic of the MOST at a low current level typically around 10 microAmp. The change of threshold voltage uniquely determines the radiation dose when “read out” at a calibrated temperature.
Another example of a prior art dosimeter is based on high energy deposited directly into a semiconductor PIN diode of material such as silicon. An example of fabrication detail for a silicon PIN diode is disclosed in U.S. Pat. No. 6,018,187 where the starting material is high resistivity (π) silicon. When a PIN diode is used as a dosimeter, deposited energy from x-ray or nuclear radiation displaces silicon atoms within the diode and creates recombination energy levels within the bandgap energy range of the semiconductor. The PIN diode is especially sensitive to damage from high energy gamma and neutron radiation. The density of the defect structures so created by energy deposited within the diode increases the reverse leakage current of the diode as the depletion region extends through the diode bulk. The change of reverse current is semi-permanent when the PIN diode is stored at room temperature. The change in reverse current leakage of the PIN diode when measured at a calibrated temperature uniquely determines the radiation dose.
In other prior art relating to the present invention structures that permit temperature control of a sensor device is disclosed in the form of micro-platforms of U.S. Pat. No. 9,236,552, U.S. Pat. No. 9,006,857, U.S. patent application Ser. No. 15/083,286 filed Mar. 29, 2016, and U.S. Pat. No. 6,091,050. Integrated electrical and phononic nanowires together with heated micro-platforms are disclosed in these patents and patent applications. This prior art is depicted in FIG. 1A, FIG. 1B, FIG. 2 and FIG. 3.
FIG. 1A depicts a prior art micro-platform 110 with nanowires 214 supported by a surrounding support platform 102 is depicted in the plan view of FIG. 1A. The micro-platform is suspended over cavity 125. In embodiments a series-connected array of thermoelectric elements 112 provide wither a Seebeck sensing or Peltier cooling function depending on the polarity of the supply voltage connected to pads 501 and 502. Another element 504 depicts a resistive structures such as a thermistor. In embodiments the micro-platform is comprised of a diffused diode 872 providing a light sensor.
FIG. 1B depicts a prior art nanowire 214 with phononic structures 104 and 105. These are phononic structures that reduce the thermal conductivity of the nanowire by phononic scattering or phononic resonance.
FIG. 2 and FIG. 3 depict prior art cross-section view of a micro-platform 110 with tetherbeams 214 comprised of an active layer 346. In these illustrative depictions the surrounding support structuring 340 includes a dielectric film 344, handle wafer 342, bonding film 354 and a header 352. A patterned metallic contact 350 is variously connected to devices located in or on the microplatform in this depiction. In FIG. 2 the cavity 125 is created by backside etching of the starting wafer. In FIG. 3 the cavity 125 is created by frontside etching of the starting wafer.
In other prior art, such as U.S. Pat. No. 7,849,727 micro-platforms are disclosed comprising a multiple-layer membrane dielectric structure without thermal-isolating nanowires.